Objective To estimate the prevalence of confirmed permanent childhood hearing impairment and its profile across age and degree of impairment in the United Kingdom. Design Retrospective total ascertainment through sources in the health and education sectors by postal questionnaire. Setting Hospital based otology and audiology departments, community health clinics, education services for hearing impaired children.

More quality of life is likely to be gained per unit of expenditure on unilateral implantation than bilateral implantation.

1. The responses of units in the ventral cochlear nucleus in anesthetized guinea pigs have been measured to best-frequency tones, noise bands geometrically centered around the unit best frequency, and noise bands asymmetrically positioned around the best frequency. 2. Each unit isolated was characterized using peristimulus time histograms (PSTHs) to best-frequency tones at 20 and 50 dB suprathreshold, frequency-intensity response areas and rate-versus-level functions in response to best-frequency tones and wideband noise. The data reported here are derived from full analyses of 5 chopper units and 17 onset units. The onsets were divided into onset-I (OnI), onset-L (OnL), and onset-C (OnC) by the criteria described by Winter and Palmer: the PSTHs of OnI units show only an onset response, OnL units respond with a single spike at onset followed by a low level of sustained activity, and OnC units have PSTHs with one to four onset peaks and low levels of sustained discharge. 3. In response to geometrically centered noise bands of constant spectral density, the discharge of chopper units and one OnI unit increased over a relatively narrow range of bandwidths, corresponding to the equivalent rectangular bandwidth calculated from their response area, and then became constant. In contrast, OnL and OnC units showed increases in discharge rate with noise bandwidth over very wide ranges of bandwidth. The growth of the discharge rate with noise bandwidth was approximately linear on double logarithmic axes and therefore could be described by a power function with an exponent of 0.37. This relation held even for noise levels near threshold. 4. When noise bands with constant spectral density (at the input to the earphone) were presented with one edge fixed at the unit's best frequency, the discharge rate of most chopper units and the one OnI unit increased over a narrow range of bandwidths and then became constant. This pattern was observed irrespective of whether the second edge of the noise was progressively increased above, or decreased below, the best frequency. For two of the chopper units, in which lateral inhibitory sidebands could be demonstrated, increasing the noise bandwidth led first to increases and then to decreases in the discharge rate as the noise energy impinged upon the sideband. The chopper units act like energy detectors with a filter corresponding to their single tone response area, but, for some units, with the addition of inhibitory sidebands. 5. For the OnL and OnC units, increasing the noise bandwidth above or below best frequency caused progressive increases in the discharge rate over wide ranges of bandwidth. These increases occurred even for low noise spectral densities. The growth in discharge rate for these onset units was well fitted at all spectral density levels by power functions: one above best frequency and one below. At levels of the noise 40 dB above the unit threshold, the point at which the discharge rate reached 90% of its maximum was, on average, about 2 octaves below best frequency and...

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The IHR-McCormick Automated Toy Discrimination Test (ATT) measures the minimum sound level at which a child can identify words presented in quiet in the sound field. This 'word-discrimination threshold' provides a direct measure of the ease with which a child can identify speech and a surrogate measure of auditory sensitivity. This paper describes steps taken to maximize the test-retest reliability of the ATT and to enable it to measure word-discrimination thresholds in noise as well as in quiet. It then describes the results of a clinical evaluation of the ATT in which paediatric audiologists measured word-discrimination thresholds in quiet from 215 successive attendees (in the age range 2 to 13 years) at a paediatric audiology clinic presenting over a 2-month period. When children with atypical cognition or delayed development of language were excluded, 72% of the children provided two word-discrimination thresholds and 83% provided at least one word-discrimination threshold. Children who failed to provide word-discrimination thresholds were generally younger than four years of age. Although a few children who could not perform pure-tone or warble-tone audiometry managed to provide word-discrimination thresholds, most children who could perform the ATT could also perform pure-tone audiometry. The average pure-tone threshold in the better-hearing ear could be predicted from the word-discrimination threshold with a 95% confidence interval of +/- 13 dB. The test-retest reliability of the ATT was measured in two ways. First, to enable comparison with published results, the within-subjects standard deviation of word-discrimination thresholds was calculated. It varied as a function of age and degree of impairment, but was never worse than 3.3 dB. Children of four years of age and older displayed the adult reliability of 2.3 dB. Second, the variability of absolute differences between word-discrimination thresholds was calculated. It was such that a change of 7 dB between two runs of the test (e.g. aided and unaided) would be expected to occur by change less than one time in 20. These results extend previous evaluations of the ATT to a clinically representative population and confirm that word-discrimination thresholds provide a useful complement to warble-tone and pure-tone audiometry.